FIG 5.

MDA-5 is the main sensor of SARS-CoV-2 in Calu-3 model cells. Calu-3-Cas9 cells were transduced with lentiviral vectors expressing CRISPR nontargeting single-guide RNAs (sgRNAs) (Ctrl #1 and Ctrl #2) or sgRNAs targeting RIG-I, MDA-5, or MAVS, and selected for 2 weeks. (A) Expression levels of RIG-I, MDA-5, and MAVS were assessed in the different populations by immunoblotting, where actin served as a loading control (a representative immunoblot is shown). (B and C) Cells were challenged with SARS-CoV-2 at MOI 0.05 and their supernatants harvested at 24 h and 48 h postinfection. Concentrations of type I (B) and type III (C) IFNs produced in the supernatants were analyzed using HEK-Blue IFN-α/β and IFN-λ reporter cells, respectively. The means of three independent experiments are shown, with error bars representing the SD from the mean.